Smithsonian.com

Paleontologists Take Another Look at a Square-Mouthed Sauropod

Sauropods were exceptionally strange creatures. With tiny heads mounted at the tip of ludicrously long necks anchored on a massive body with tapering tails on the other end, they were truly marvels of evolution. As odd as the basic sauropod body plan was, though, many sauropods had armor, clubs, sails and other features which only added to their unique character. Among them was Bonitasaura, a roughly 83-million-year-old "beaked" sauropod from Argentina.

Bonitasaura was originally described in 2004, but now paleontologists Pablo Gallina and Sebastián Apesteguía have redescribed its skull with more recently discovered fragments in a report to be published at Acta Palaeontologica Polonica. This peculiar dinosaur was a member of the widespread group of Cretaceous sauropods called titanosaurs, and these sauropods proliferated in South America and elsewhere during a time when North America was devoid of the classic sauropod communities that had thrived during the Late Jurassic. Despite what scientists have learned about titanosaurs in the past few decades, however, we still know relatively little about their skulls. As with sauropods in general, titanosaur skulls are seldom found, and the discovery of skull material from Bonitasaura offers a rare perspective on the diversity of head shapes among these giants.

Gallina and Apesteguía did not have a complete, articulated skull to work with. Instead only bits and pieces of the skull were found, each part of an osteological puzzle that was this animal's head. When put all together, though, the general shape of the skull could be ascertained, and the paleontologists found that Bonitasaura had a skull that was short from front to back, with a squared muzzle that flared out to the sides. (Superficially, the skull vaguely resembled that of Nigersaurus, a distantly related sauropod cousin with a head like a Hoover vacuum. While the authors do not mention Nigersaurus specifically, they note that this jaw type now appears to have evolved independently in different groups of sauropods.) Furthermore, as pointed out in the original description, this dinosaur did not have a beak like a parrot or hadrosaur, but instead possessed a sheath of keratin on its jaws behind its teeth, which may have created a sharp cutting edge for processing plant food.

The skull shape of Bonitasaura differs from the long and low skulls of other titanosaurs, and the new characteristics seen among elements prepared since the dinosaur's initial description has allowed it to be grouped with other titanosaurs such as Mendozasaurus, Antarctosaurus and—what surely must be a top contender for the more tongue-twisting dinosaur name—Futalognkosaurus. Frustratingly, the precise relationships of these sauropods are still blurry, and hopefully future discoveries will bring resolution to the sauropod family tree.

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